Crane hoist control



July 16, 1940. Q E STQLTZ 2,208,401

CRANE HOIST CONTROL Filed May 16, 1939 2 Sheets-Sheet l lo Q u i LQ L3 9in m Q u l 5?, fb n) l u I ,p U sa l u I a in u.. ll Q51ml! Q' 4? w m NP N \D Ik Q x im N ATTORNEY July 16, 1940- G. E. sToLTz CRANE HOISTCONTROL Filed May 16, 1939 2 vSheetS-Sheet M/ZZ Cun/e151 /00 80 6o 40 zo0 Za 4o 60 490 wlTNEssEs:

INVENTOR /enn 50/ IZ- ATTORNEY O O O O O Patented July 16, 1940 UNITEDSTATES PATENT OFFC CRANE HOIST CONTROL East ittsburgh, Pa.,

Sylvania a corporation ot Penn- Application May 16, 1939, Serial No.273,851

9 Claims.

My invention relates to a control system for an electric motor and isparticularly applicable to a motor utilized for operating load hoistingor elevating devices "or load lowering devices such 5 as cranes and thelike.

An object of my invention is to provide a system or control thatembodies a minimum number of units and which is simple and reliable inoperation, and is inexpensive to manufacture.

l0 Another object of my invention is to provide a control system whichhas substantially ideal or most desirable speed torque curves for ahoist motor when operating in the lowering direction.

A more specific object of my invention is to 13 provide amotor-generator set used as a booster to boost the eld strength of themain motor when the main motor is regenerating current due to anoverhauling load in the lowering direction and, in effect, is acting asa generator and which motor generator is inoperative when the main orhoist motor is acting as a motor either in the lowering or hoistingoperation. l

Other objects and advantages will become more apparent from a study ofthe following specification when considered in conjunction with theaccompanying drawings, in which:v

Figure 1 is a diagrammatic showing of a complete system of controlembodying my invention;

Fig. 2 shows the motor circuit for the fifth controller position ofhoisting;

Fig. 3 shows the motor circuit for the th controller position during thelowering operation;

Fig. 4 shows a series of samples of speed torque curves for controlsystems conventional in the art for all the controller positions of themotor when the motor is operating in the lowering direction; and

Fig. 5 is a sequence chart shownig the sequence n circuits both for thehoisting and the lowering operation.

In a crane hoist control it lls desirable to obtain as high a speed aspossiblefor the crane hook when lowering empty, and at the same time notobtain an excessive speed when lowering with a heavy load. Referring tothe speed torque curves in Fig. 4, which are illustrative of controlsystems when the load is overhauling, the hoist motor is used to developa braking torque, the figure showing that with 63% field current theincrease in speed with load is appreciable but not dangerous. The figurealso shows the performance of the motor in one instance with 37% fieldcurrent and another with 24% iield 22 of the booster generator G.

of operation in the various switches in the motor field current, wherewith less than full load on the hook, the hoist motor would run away.

In accordance with my invention the above mentioned runaway conditionwill be eliminated and the speed torque curves for low values of f.field current will be substantially ilattened, very much like thoseillustrating 44% and 63% field current.

Referring more particularly to Figure i of the drawings, M designates ahoist motor (of the series type), which is to be controlled and B and F,respectively, designate the brake winding and field winding. M' and G'designate the units oi the motor-generator set, which set is used as abooster. Associated with the motor of the i5 motor-generator set is afield coil 253 and a conventional control rheostat 2|. The generator Gof the motor-generator set has a field winding 22, a conventionalcontrol rheostat 23 and a rectler unit, preferably of the copper oxidetype, 26, all of which are connected in shunt across a resistance R,which resistance is permanently in series with the armature or motor.lr/i. Since it will be logical to place the motor-generator set used asa booster on or near the crane cab with the control, resistance R isinstalled in the lead of the armature of the hoist motor, from whichwill be shunted current to excite the The voltage of the generatorshould then be proportional to the loads taken by the armature up to thepoint where the field of the booster saturates. it not essential thatthe booster voltage be dire1 proportional to the armature current of thehoist motor, but it will be necessary to design booster so that it doesnot saturate at too low load. The rectier unit 2c is placed in thecircuit of the booster generator so thatrcurr it will flow in the iielolof the booster generator only f when the load is heavy enough to causethe hoist armature to regenerate and, in eiect, act as generator. Whenthe hoist armature is heilig accelerated or when the ioad is so low thatthe hoist motor operating as a motor, the flow of current wili 'se inthe opposite direction the rectifier unit 2li will prevent current nos.'in the elcl 22 of the booster so that the l: will have no modifyingeiiect on the field oi Sie main motor when the latter is acting as amoto in the lowering direction.

Since this booster eiiect of the crane motor Viele is only wanted in thelowering direction, t

armature of the booster will be connected in th held circuit of thehoist motor in such a manner 35 that it will be in the circuit onlyduring the lowering direction.

A control system is illustrated for the motor and is shown in thedeenergized position. A controller C which may be of any desirable typesuch as the drum type and has a plurality of Contact segments forvarying the circuit connections for different positions in the hoistingor lowering direction. Five positions are shown in the hoistingdirection and five positions are also shown in the lowering directionfor giving various values of speed and torque to the motor in thesedirections. Contact members I to II, inclusive, and I6 (and Ic) areoperable by relays IA to IIA, inclusive, and ISA respectively to securevarious circuit combinations in the hoisting and lowering directions.Contact members I2 and I2C, I3, I and Ib, inclusive, are operable bytime limit relays IZA to IA, inclusive, respectively. The time limitrelays I2A to ISA, inclusive, have main coils I2M to lM, inclusive, andneutralizing coils l2N to I5N, inclusive, respectively. Each of theserelays is biased in one direction by a spring as shown. A relay rheostat26 is provided for adjusting a time constant of the relays. It will benoted that the springs associated with each of the relays is alsoadjustable thereby providing additional adjusta bility of the timeconstant of the relays. The operation of these time limit relays formsno part of my invention, but to briefly describe their operai tion itmay be generally\ stated that relay I2A holds one of its associatedcontact members I2 closed in the lowering operation, due to the timedelay of coil l2N, long enough to insure release of the brake bymaintaining relay 5A energized to close contact members 5, and preventsclosing of contact members I8 in the lowering direction until contactmembers I2 are open. Time limit relay I3A picks up on the fourth pointlowering and holds its contact members I3 closed thereby completing acircuit to energize coil 6A and close contact members Iii to insureenergization or' relay l IA which closes contact members I I to providea regular braking circuit, and to open contact members tto preventapplication of the emergency braln'ng circuit for a fraction of a secondif the master switch is returned suddenly to the off position.

By referring to Fig. 5, which is a sequence chart showing the sequenceof operation of the various switches in the motor circuits for bothhoisting and lowering operations, the particular circuit for any oi thefive positions of hoisting or lowering can be identified. Inasmuch as myinvention is not concerned with the successive steps or positions in theoperation of the motor either in the hoisting or in the loweringdirection, it is deemed that a detailed explanation of each successiveposition in hoisting or lowering is unnecessary. Furthermore, thecontrol system illustrated in the iigures together with the sequencechart in Fig. 5 will readily disclose to those familiar with the artwhat the various circuit in each successive position in hoisting orlowering consists of.

operative since it is omitted from the circuit and all of the fieldcoils together with the braking field coil are connected in series withthe inf coming power line, hence the motor operates as a series motor.Fig. 2 shows the fth position of hoisting and is illustrative of thisseries connection. 0n the other hand, on all five positions of lowering,the motor generator set M', G', together with its associated parts, isincluded in the circuit. Furthermore, on all ve positions of lowering,the field coil F and the brake coil B are connected in parallel with themotor armature M so that the motor is now acting as a shunt motor. Fig.3 which shows the fifth position of lowering is illustrative of theshunt connection. In the hoisting operation the full value of startingresistance is connected in series with the various field coils, brakecoil and motor armature and, in general, in going through the vesuccessive steps, the starting resistance is gradually shunted out. bysuccessive increments until finally, as shown in Fig. 2 representing thefth hoisting position, the starting resistance is completely shunted outand the motor with its various I'ield coils and brake coil is connecteddirectly across the line. On the other hand, in the lower operation ingoing from the first tothe fth position, resistance is graduallyinserted in series withthe shunt field in successively greater amountsuntil finally, as will be noted from Fig. 3 illustrating the fifthlowering position, the full value of resistance is inserted in serieswith the shunt field. As it will be obvious to those skilled in theelectrical art, as the resistance is gradually decreased in going fromthe first to the fifth position in the hoisting operation of a constantload when the motor M is connected as a series motor, the speed andtorque thereof will gradually increase. On the other hand, in thelowering operation, as the resistance in series with the shunt ield isgradually increased so as'to gradually weaken the shunt eld, the speedof the motor gradually 1ncreases and the torque decreases.

My invention is specically directed to the use of a boostermotor-*generator set in the lowering operation of the main hoist motor.When light loads are lowered and the main motor is acting as a motor, noshunt current will traverse the field coil Y22, because of the blockingaction of rectifier 25j However, on heavier loads in the loweringdirection, which are sufficient to cause the motor to overhaul andregenerate current in the opposite direction of the normal motorcurrent, a shunt current will flow through the generator field coil 22in an opposite direction and will no longer be arrested by rectifier 26,and this boosting current will strengthen the main eld F to such anextent as to cause the speed to increase less rapidly with increasingloads, or to remain substantially constant or even decrease, dependingon the ampere turns of field coil 22.

These characteristics will become more apparent in tracing the circuit.When light loads are lowered and the main motor M is acting as a motor,the main circuit may be traced, in Figs. 1 and 3, from the terminalmarked (-l) through bridged contact members 2, motor M, resistor R,bridged contact members l, 9 and 8, respectively, to the negativeterminal marked Connected in parallel toresistor R, is another circuitincluding rheostat 23, field coil 22 (of generator G of the boostermotor-generator set) and rectier 24. However, inasmuch as the flow ofcurrent is of from left to right through resistor R, the recticr 24 willarrest current fiow through Y the parallel path. However, if a load isbeing lowered that is sufficiently heavy so as to cause motor M tooverhaul, then current will be regenerated by motor M in the abovetraced main circuit but in an opposite direction dueto the fact that themotor M is now acting, in effect, as a generator. Inasmuch as thisregenerated current may be greater than the normal flow of supplycurrent (previously traced) but opposite in direction, the resultantcurrent will flow through resistance R in a direction from right toleft. Now current will flow through the paralle] path includingrectifier 24, booster generator field coil 22 and rheostat 23 due to themanner in which rectifier 24 is connected, as the result of whichgenerator G' will start to generate a voltage in the direction indicatedby the arrow. A main shunt path may now be traced from the terminalmarked through bridged contact members 2, field coil F, brake coil B,resistors R2 and Re, the armature of generator G', bridged contactmembers IBc, II, 9 and 8 successively to the negative terminal It willthus be seen that as the current regenerated by motor M increases, thecurrent through field winding 22 increases and the voltage developedacross the armature of generator increases therefore boosting thecurrent flow through the main shunt path (i. e., through field coil F)hence tending to decrease the speed of motor M. It will be noted thatthe main shunt path is the same during lowering light loads during whichmotor M is acting as a motor, that is, it includes the armatureofgenerator G', however, since no voltage is developed across'thisarmature (since no current is flowing through the field coil 22 due tothe arresting action of rectiiier 24) no additional current Will be sentthrough the main shunt circuit through field coil F, hence there will beno modifying or boosting action on While I have described the motorgenerator set as being in the circuit in all positions or lowering, itwill be obvioous that it is also possible, instead, to have themotor-generator set in circult only in a few of the ultimate positionsof lowering, say for example, in the fourth and fifth positions only oflowering. In other words, it is recognized that the most important useof the booster is in the latter positions or the last position oflowering. The necessary change in the circuit connections foraccomplishing this will be obvious to those skilled in the art. Also, ifthe booster is put in other than the fifth point such as the fourth orthird, its effect can be decreased. This will be partially automatic asthe motor field approaches saturation. this alternate arrangement isrecognized, it is felt that the preferable and most simple circuitconnection would be that as previously described, since a minimum numberof contactors is used, that is, the arrangement by which themotorgenerator is kept in circuit throughout the entire loweringoperation.

On cranes it is desirable only to prevent the load and motor fromrunning away under heavy loads, the value of the booster can be selectedto keep the speed torque curves flat, approximately as shown in Fig. 4for 63% and 44% ield amperes. On other applications where it may bedesirable to have a lower speed load condition than with empty hook, thevalue of the booster can be increased so that the speed torque curvesdrop oir with increased loads.

My control system is a substantial improvement over the well knowncontrol systems employing relays and the like wherein abrupt changes aresecured for the purpose of checking excessively high speed but whichabrupt changes of: (fri are detrimental to safe operation ci a cranehoist. Obviously any sudden change in the speed of the crane either inthe raising or lowering position might cause a shaking off of the loaddangerous and at the of the crane would be very confusing and difficult.

Many protective features usually embodied in control systems of thiskind such as an overload and undervoltage protection have been omittedfor the sake of simplicity, but it is understood, of course, that thesefeatures may be incorporated in the above described control system.

I am, of course, aware that others, particularly after having had thebenet of the teachings of my invention, may devise other devicesembodying my invention, and I, therefore, do not wish to be limited tothe specilic showings made in the drawings and the descriptivedisclosure hereinbefore made,

prior art that may be pertinent.

I claim as my invention: l. A control system for a hoist motorcomprising, in combination, a hoist motor, circuit means :for a hoistmotor compriscontinuously and directly boosting the iield ,f

strength of said motor in accordance with the load oi said motor toeiect slowing down of said motor.

3. A control system for a hoist motor comprising, in combination, ahoist motor, circuit means for energizing said motor to ei'l'ect ahoisting or lowering operation, said motor, having a field coil which isconnected in shunt therewith during lowering operation of the motor, abooster generator which is effective during the lowering operation only,of' said motor for boosting the eld strength thereof and for effectingslowing down of said motor.

4. A control system for a hoist motor for a crane or the likecomprising, in combination,

hoist motor including a iield coil, circuit means for energizing saidmotor to effect either a hoisting or lowering operation, a boostergenerator having a leldrcoil which is effective to compensate said motorfield relation `with the armature of said motor so that the voltageimpressed on said booster generator neld coil is proportional to theload current flowing through the armature of said hoist motor.

5. A control system for a hoist motor for a crane or the like comprisingi combination, a hoist motor, including a iield coil circuit means forenergizing said motor to either a hoisting or lowering operation, abooster generator having a field coil which durinf at least a part ofthe lowering operation, of said motor is in circuit relation with thearmature ci said mctor so that the voltage impressed on said boostergenerator eld coil is proportional to the load current flowing throughthe hoist motor, circuit means coil and which is in circuit a:

armature of said t hoist motor, rectier meins in circuit relation withsaid field coil which allows current flow only in the direction of flowof regenerated current developed in said armature due to an overhaulingload, and which-is not conductive to current flowing through saidarmature when said motor is operating as a motor. Y

6. A control system for a hoistA motor for a crane or the likecomprising, in combination, a hoist motor including a field coll,circuit means for energizing said motor to eiect either` a holsting orlowering operation, a. booster generator having a field coil whichduring the entire lowering operation, only, of said motor is in circuitrelation with the armature of said motor so that the voltage impressedon said booster generator iield coil is proportional to the load currentowing through Ythe armature of said hoist motor, rectifier means inseries with said eld coil which allows current flow only in thedirection of flow of regenerated current developed as the result ofgenerator action ofV said motor during an overhauling load, and which isnot conductive to current flow through said armature when said.

motor is operating as a motor.

7. A control system for a holst motor for a crane or the likecomprising, in combination, a

hoit motorV including a eld'coil, circuit means for energizing saidmotor, to effect either a hoisting or lowering operation, a resistor,whichl may be a series winding or lead of the hoist motor armature inseries with the amature of said motor, a motor-generator booster sethaving a generatoriield, rectifier means connected in seriesrelationship with said booster generator field and said rectier meansand booster generator field being connected in shunt with said resistor,said motor-generator boster set being operable to compensate the eldcoil of said hoist motor only during lowering operation of said motor,said rectifier means allowing flow of current deveioped by regenerationof said motor due to its generator action during overhauling loads andimpeding the flow of motor current in said armature when said motor isacting as a motor.

8. A control system for a hoist motor for a crane. derrick or the likecomprising, in combination, a hoistmotor including a field coil, circuitmeans for energizing said motor, to eect either a hoisting or loweringoperation, a resistor in series with the armature of said motor, amotor-generator booster set having a generator eld, rectier meansconnected in series relationship with said booster generator eld, andsaid rectifier means and booster generator iield being connected inshunt with said resistor, said motorgenerator booster set being operableto compenvsate the iield coil of said hoist motor only during loweringoperation of said motor and during at least a part of said loweringoperation, said rectifier means allowing flow of current developed byregeneration of said motor due to its generator action duringoverhauling loads in the lowering direction and impeding the flow ofmotor current in said armature when said motor is acting as a motor.

9. A control system for a hoist motor for a crane or the likecomprising, in combination, a

hoist motor including a eld coil, circuit means for energizing saidmotor, to eiect either a hoisting or lowering operation, a resistor inseries withV the armature of said motor, a motor-generator booster sethaving a generator field, rectifier means connected in seriesrelationship with said booster generator field, and said rectier meansand booster generator field being connected in shunt with said resistor,said motor-generator booster set being operable to compensate the ieldcoil of said hoist motor only during lowering operation of said motor,saidrectier means allow- Ving fiow of current developed by regenerationof said motor due to its generator action during overhauling loads andimpeding the iiow of current in the booster eld when said motor isacting as a motor, said hoist motor including a ileld Y coil which isconnected in series relation with said booster armature thereof duringlowering operation, said booster generator being effective duringlowering operation with an overhauling load to increase the fieldstrength of said hoist motor field thereby slowing down said motor.

, GLENN E. STOLTZ.

